Vaccinia virus is a member of the poxvirus family of DNA viruses. Poxviruses including vaccinia virus are extensively used as expression vectors since the recombinant viruses are relatively easy to isolate, have a wide host range, and can accommodate large amounts of DNA.
The vaccinia virus genome contains nonessential regions into which exogenous DNA can be incorporated. Exogenous DNA can be inserted into the vaccinia virus genome by well-known methods of homologous recombination. The resulting recombinant vaccinia viruses are useful as vaccines and anticancer agents.
The use of vaccinia virus recombinants as expression vectors and particularly as vaccines and anticancer agents raises safety considerations associated with introducing live recombinant viruses into the environment. Virulence of vaccinia virus recombinants in a variety of host systems has been attenuated by the deletion or inactivation of certain vaccinia virus genes that are nonessential for virus growth. However, there remains a need in the art for the development of vectors that have reduced pathogenicity while maintaining desirable properties of wild-type virus, such as host range, and active protein synthesis of a desired gene product.
The present invention provides a recombinant vaccinia virus in which the vaccinia virus E3L gene is replaced by a gene encoding an E3L homolog from the orf virus. The invention further provides an expression vector comprising the recombinant vaccinia virus and exogenous DNA, and methods of use of the recombinant vaccinia virus.